1. Field of the Invention
The present invention relates to an X-ray image pickup apparatus and, more particularly, to a compact X-ray image pickup apparatus which is inserted into an oral cavity and used for intraoral radiograph taking a X-ray image of a dentition.
2. Related Background Art
In dental treatment, an intraoral X-ray imaging system using a solid-state image sensing device such as a CCD (Charge Coupled Device) is widely used to obtain an X-ray photographic image of the oral cavity, and particularly, a dentition. This X-ray photographic image is called an intraoral radiograph.
A conventional intraoral X-ray imaging system is disclosed in, e.g., Japanese Patent Laid-Open No. 7-280944. FIG. 5 is a view showing the entire arrangement of this system. FIGS. 6A to 6C are sectional views showing some X-ray image pickup apparatuses used in this system.
As shown in FIG. 5, an X-ray source 20 for irradiating a beam of X-rays and an X-ray image pickup apparatus 22 for intraoral radiograph are opposed each other while sandwiching a dentition 21 of a patient as a subject. The X-ray image pickup apparatus 22 is connected to a control unit 24 for controlling the entire system, through a cable 23 for transmitting image signals and supplying driving power. The control unit 24 is also connected to a monitor 25 for displaying the X-ray photographic image and a printer 26 for printing the displayed image.
The internal structure of the X-ray image pickup apparatus 22 will be described next with reference to FIGS. 6A to 6C. FIG. 6A is a cross-sectional view of the X-ray image pickup apparatus viewed from the direction of X-ray beam incident surface. FIG. 6B is a longitudinal sectional view including the cable portion. FIG. 6A corresponds to a section taken along a line A--A in FIG. 6B, and FIG. 6B corresponds to a section taken along a line B--B in FIG. 6A. FIG. 6C is a sectional view taken along the line B--B of the apparatus shown in FIG. 6A when the cable 23 is extracted from a surface opposite to the X-ray beam incident surface.
In the X-ray image pickup apparatus 22, a phosphor 1 for emitting visible light in response to x-ray incidence, an optical fiber plate 2 for transmitting the resulting visible light image, a CCD 3 for converting the transmitted visible light image into an electrical signal, a substrate 5 supporting the CCD 3 et al., and an X-ray shielding member 4 using lead or the like to absorb the X-ray and prevent it from passing through the surface opposite to the X-ray incident surface are stacked and sealed in a container 14 consisting of a synthetic resin having insulating and light-shielding properties. The cable 23 for extracting the output electrical signal from the CCD 3 and supplying driving power is electrically connected to the CCD 3 and extracted outward from the side surface or lower surface of the container 14, as shown in FIG. 6B or 6C.
The operation of this conventional apparatus will be described next with reference to FIGS. 5 and 6A to 6C. As shown in FIG. 5, X-rays emitted from the X-ray source 20 are partially interrupted by the dentition 21 and the silhouette image of this are projected on the incident surface of X-ray image pickup apparatus 22. In the X-ray image pickup apparatus 22 shown in FIGS. 6A to 6C, the incident X-rays are transmitted through the container 14 and absorbed by the phosphor 1. The phosphor emits the visible light corresponding to the intensity of incident X-rays. That is, a visible light image corresponding to the X-ray silhouette image is obtained. This visible light image is guided to the CCD 3 through the optical fiber plate 2. The CCD 3 has two-dimensionally arrayed pixels, so incident light is converted into an electrical signal in units of pixels. Of the X-ray components which have not been absorbed, X-ray components which have passed through the container 14, the phosphor 1, the optical fiber plate 2, the CCD 3, and the substrate 5 reach the X-ray shielding member 4 so most components are absorbed. For this reason, the amount of X-ray emerging from the lower surface of the container 14 is suppressed, so the exposed dose of the patient is minimized. Degradation in image caused when X-ray components which have been transmitted through the lower surface of the apparatus and reflected by another member are incident again from the lower surface can also be prevented.
The output electrical signal from the CCD 3 is sent to the control unit 24 through the cable 23 and processed image corresponding to the X-ray silhouette image of the dentition (intraoral radiograph) is displayed on the monitor 25, as shown in FIG. 5. In addition, a desired image can be printed out using the printer 26.
Japanese Patent Laid-Open No. 2-10973 discloses a technique of directly forming a phosphor on a solid-state image sensing device without using any optical fiber plate. With this technique, an X-ray incident on an apparatus 22 is transmitted through an incident window 31 and absorbed by a phosphor 1. Since the fluorescent light can be directly converted into an electrical signal by a CCD 3, no optical fiber plate is required, and the apparatus can be made compact. An X-ray shielding member 4 consisting of a polyimide resin and having a thickness of 1 mm is formed on the X-ray incident surface side excluding the incident window 31.